Assembly for deaeration of liquids

ABSTRACT

A deaeration assembly for removal of air or other gases dissolved in a liquid. The assembly includes a deaeration element having a gas-channel-forming component enclosed and sealed within an envelope which includes a nonporous fluoropolymer film. The assembly also includes a liquid-channel-forming component which can be positioned on the outside of the element, or can be enclosed with the gas-channel-forming component within the element. The assembly can be formed in spiral-wound or folded configurations for installation in a deaeration module or apparatus. The deaeration assembly is useful for removal of gases dissolved in chemically aggressive liquids, high-purity liquids, and other special liquids.

This application is a continuation-in-part of application Ser. No.08/804,769, filed Feb. 24, 1997, now U.S. Pat. No. 5,830,261.

FIELD OF THE INVENTION

The present invention relates to apparatus for deaeration of liquids,more particularly, to an assembly for removing a gas that is dissolvedin a liquid.

BACKGROUND OF THE INVENTION

That corrosive, oxidative, reactive, and contaminating propertiesharmful to certain products and equipment is associated with air orother gases dissolved in liquids is well known. To reduce or minimizethese harmful effects are among many reasons why it is sometimesdesirable to remove air and/or other gases dissolved in a liquid.

Known apparatus for performing such deaeration or degassing operationsare modules which use a porous polymeric membrane material through whichthe dissolved gas can permeate as the means for removing the gas fromthe liquid. Typically, in this type of apparatus, deaeration isaccomplished by having one side of the membrane contact the liquid to bedeaerated, and on the other side of the membrane provide a gas channel,usually under reduced pressure, to draw away the gas permeating throughthe membrane. Such systems are quite effective in deaerating water ofnormal purity.

However, a problem with the above-mentioned deaeration apparatus inwhich a porous polymeric membrane material is used is that, when theliquid to be deaerated is a solvent, a liquid fat or oil, or an aqueousliquid that contains a surfactant, the liquid tends to wet the membranematerial and penetrate through the pores, thus precluding deaeration.

In an effort to solve this problem, there have been proposals for adeaeration apparatus that makes use of a nonporous membrane material,for example, one obtained by coating the surface of a porous polymericsupport membrane with a silicone resin, or other polymer resin throughwhich gases can permeate at acceptable rates. While this apparatus doesindeed allow deaeration to be performed when the liquid to be deaeratedis a relatively mild solvent, liquid fat or oil, or aqueous liquid thatcontains a surfactant, they are not successfully used when the liquid tobe deaerated is of exceptionally high purity or is chemicallyaggressive. For example, liquids such as the deionized water requiredfor semiconductor processing, or special liquids such as photoresistliquids or developing fluids used in the manufacture of semiconductorproducts. Such liquids tend to leach substances from the separationmembranes which then contaminate the liquids; or the liquids may causethe membranes to degrade and fail.

An object of the present invention is to provide an assembly for use ina deaeration apparatus with which such special high purity andaggressive liquids can be deaerated.

SUMMARY OF THE INVENTION

The invention provides a deaeration assembly for use in a deaerationapparatus or module which resists attack by high purity or aggressiveliquids, and which minimizes leaching of materials from the assemblywhich can harmfully contaminate the liquid to be deaerated.

The deaeration assembly for removal of a gas from a liquid comprises adeaeration element having a gas-channel-forming component enclosed andsealed within an envelope formed of a nonporous fluoropolymer film, orformed of a nonporous fluoropolymer film laminated to a porous supportfilm. In either case, the outward-facing surface of the envelope is anonporous fluoropolymer surface. In use, liquid to be deaerated ispassed over an outward-facing surface of the element at a pressurehigher than the pressure inside the element. The gas channels formed bythe gas-channel-forming component provide pathways through the inside ofthe envelope for gases which have permeated from the liquid into theenvelope, to a port in the film envelope which is connected to means fortransfer of gases to a location external to the apparatus. The assemblyfurther comprises a liquid-channel-forming component, contiguous with atleast one outward-facing surface of the fluoropolymer envelope, whichprovides pathways for liquid to pass over and to contact theoutward-facing surface of the element. When the element is formed into aspiral or folded structure, the liquid-channel-forming component alsoserves as a spacer between adjacent layers of the element.

In another embodiment of the invention the gas-channel-forming componentand liquid-channel-forming component are both enclosed within thenonporous fluoropolymer envelope. In this embodiment theliquid-channel-forming component is contiguous with at least oneinward-facing surface of the fluoropolymer envelope. The portions of thefluoropolymer envelope contiguous with the liquid-channel-formingcomponent conform to the liquid-channel-forming contours of thechannel-forming component and thereby form liquid channels in theoutward-facing surface of that portion of the element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the element containing agas-channel-forming component enclosed by an envelope having anunreinforced edge seal.

FIG. 2 is a partial cross-sectional view of the element with an envelopehaving a reinforced edge seal.

FIG. 3 is a cross-sectional view of a gas-channel-forming component.

FIG. 4 is a cross-sectional view of a deaeration element containing agas-channel-forming component.

FIG. 5 is a cross-sectional view of an example of a connection between agas removal tube and the envelope at a port in the envelope.

FIG. 6 shows a spirally-wound element with a liquid-channel-formingcomponent interposed between adjacent outer surfaces of the element.

FIG. 7 shows a folded element with a liquid-channel-forming componentinterposed between adjacent outer surfaces of the element.

FIG. 8 is a cross-sectional view of a module containing an embodiment ofthe assembly of the invention.

FIG. 9 is a partial cross-sectional and perspective view of a deaerationelement in which both the gas-channel-forming component andliquid-channel-forming component are contained within the envelope.

FIG. 10 is a partial cross-sectional view of adjacent element layers ofanother deaeration element in which both the gas-channel-formingcomponent and liquid-channel-forming component are contained within theenvelope.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the figures, the invention will be described indetail. To facilitate understanding, the same numerical identifiers forelements common to the figures will be used throughout the figures.

The term "unonporous" is used herein simply to describe a material whichis essentially free of pores or voids, and which is a barrier to bulkflow of liquids or gases.

While a material may be nonporous, it may still be "permeable" toliquids or gases. The term "permeable", (and correspondingly"impermeable"), or a variation thereof, is used herein to describe theproperty of a material to transport (or not transport) a particularspecies, such as gas or water-vapor, through the material. The termdescribes the overall property of mass transfer by diffusion at amolecular level, and in no way implies any particular scientificmechanism by which this occurs.

In FIG. 1 is shown a cross-section of a deaeration element 1 whichincludes a nonporous fluoropolymer envelope 4. The envelope 4 can bemade of a single sheet of nonporous fluoropolymer film, or made of anonporous fluoropolymer film laminated to a porous support film. Theenvelope encloses a porous gas-channel-forming material 2 on each sideof which is laminated a porous polymeric membrane 3. The overlappingedges of the fluoropolymer film envelope 4 are sealed at an edge region5 which extends along the length and across the ends of the deaerationelement 1.

Nonporous fluoropolymer films are used in making the envelope 4 of thedeaeration element 1 due to their well known chemical inertness, i.e.,they are highly resistant to attack by aggressive chemicals, solvents,oils, and high purity water or other aqueous liquids, and therebyminimize contamination of liquids in contact with them. Manyfluoropolymers can be used so long as nonporous films made of them havesufficient chemical resistance to the liquids to which they will beexposed and are sufficiently permeable by the gases dissolved orentrained in the liquids. Preferably, the fluoropolymers aremelt-processible thermoplastic fluoropolymers such astetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-(perfluoroalkyl) vinyl ether copolymer (PFA),amorphous fluoropolymers, such as TEFLON AF® amorphous fluoropolymer,and the like. Such fluoropolymers are well know in the art and arereadily available in sheet and film form from a number of suppliers.

The thickness of the nonporous fluoropolymer film influences propertiessuch as gas permeation rate, strength, processability, durability inuse, etc., and may necessitate some compromise or trade-offs betweendesired properties. The nonporous fluoropolymer film used in making theenvelope 4 should be in the range 1 to 100 micrometers thick, preferablyin the range 10 to 40 micrometers thick if unsupported; or in the range0.7 to 20 micrometers, preferably in the range 1 to 5 micrometers ifsupported. When unsupported, if the nonporous fluoropolymer film is lessthan about 5 micrometers thick, it will be difficult to handle and willlack pressure resistance and durability in use. When supported, forexample, by lamination to a porous polytetrafluoroethylene film, thenonporous fluoropolymer can be as thin as 1 micrometer or less. On theother hand, if the film is thicker than about 100 micrometers, gaspermeation rates through the film may be too low to be useful.

Envelope 4 can also be made of a composite sheet comprising a nonporousfluoropolymer film laminated to a porous support film or fabric. Theporous support must have excellent mechanical strength, flexibility,pliancy, and surface smoothness. Suitable materials for the supportinclude woven, knit, or nonwoven fabrics, or films, open-cell foams,mesh, and the like, of polyethylene, polypropylene, polyester,polyurethane, fluoropolymers, and the like. Preferably the poroussupport material is a fluoropolymer, most preferably porouspolytetrafluoroethylene sheet or film. The support material should be inthe range 1 to 100 micrometers thick, preferably in the range about 20to 40 micrometers thick. Support material thinner than 1 micrometerthick is too weak, and material thicker than about 100 micrometers aretoo bulky, unnecessarily increasing the size of the element.

Porous polytetrafluoroethylene sheet or film suitable for use in theinvention can be made by processes known in the art, for example, bystretching or drawing processes, by papermaking processes, by processesin which filler materials are incorporated with the PTFE resin and whichare subsequently removed to leave a porous structure, or by powdersintering processes. Preferably the porous polytetrafluoroethylene filmis a porous expanded polytetrafluoroethylene film having a structure ofinterconnected nodes and fibrils, as described in U.S. Pat. Nos.3,953,566 and 4,187,390 which describe the preferred material andprocesses for making them.

The porous polytetrafluoroethylene membrane should have a pore volume inthe range of about 30 to 95 percent, a nominal pore size in the range ofabout 0.1 to 100 micrometers, and be about 5 to about 100 micrometersthick. Lamination of the nonporous fluoropolymer film to the porouspolytetrafluoroethylene support film can be done using conventionalmethods and equipment, for example, by adhesive bonding. The adhesivecan be applied to the surface to be bonded of either layer, and shouldbe applied in a noncontinuous pattern. A noncontinuous pattern ofadhesive is used herein to indicate a layer of adhesive which is appliedto a surface so as to not form a nonporous continuous film. For example,a layer applied to a surface as a pattern of discrete dots, a porousnon-woven web or mesh, or the like.

Lamination of the nonporous fluoropolymer film to a porouspolytetrafluoroethylene support is preferably done using conventionalheat fusion methods and equipment whereby the nonporous fluoropolymerfilm is adhered to the support membrane, for example, by application ofheat and pressure by heated platens, or by passage through the nip ofheated calender rolls. The temperature of the platens or rolls should bein the range between the softening point to slightly above the melttemperature of the melt-processible fluoropolymer, for example, forfilms of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) andtetrafluoroethylene-(perfluoroalkyl) vinyl ether copolymer (PFA), thetemperatures should be in the range about 240° C. to 315° C. Goodbonding of the melt-processible fluoropolymer to the support membrane isobtained by slight penetration of the melt-processible fluoropolymerinto the surface regions of the porous polytetrafluoroethylene film toform interlocking mechanical bonds in the porous structure. Thecomposite fluoropolymer film thus made can be used as laminated or canbe further stretched to form a thinner film having a higher gaspermeation rate.

If a thinner film is desired, the composite material formed of thenonporous fluoropolymer film and support membrane can be heated to atemperature near or slightly above the melt point of themelt-processible fluoropolymer and stretched uniaxially or biaxially inthe planar directions. Stretching may be done using conventionalequipment or apparatus known in the art. For example, stretchingequipment such as differential speed rolls for stretching in the machinedirection (MD) and tenter frames for stretching in the transversedirection (TD) can be used. Stretching in two directions may be donesimultaneously or sequentially, and may be done in one or more steps.The amount of stretch, relative to original dimensions in the planar x-ydirections is ordinarily in the range 1.5 to 15:1. As the compositefluoropolymer film is stretched in the planar x-y directions the area ofits surface progressively increases and its thickness is progressivelyreduced. At the same time, as there is no change in the volume ofmelt-processible fluoropolymer, the nonporous fluoropolymer film becomesprogressively thinner as the material of the film is dragged and spreadby the stretching membrane.

Such composite stretched films are preferably formed by laminating anonporous melt-processible fluoropolymer film, such as a FEP or PFA film10 to 100 micrometers thick, to a porous polytetrafluoroethylene film 20to 200 micrometers thick. The composite film is then stretched in one ortwo directions an amount of about 1.5-15 to 1 at a temperature in therange about 240° C. to 315° C. After stretching, the thickness of thenonporous film is in the range about 0.7 to 50 micrometers thick,preferably in the range about 1 to 20 micrometers thick. The thicknessof the porous polytetrafluoroethylene film is reduced to about 1.3 to100 micrometers thick, preferably in the range 5 to 50 micrometersthick. The stretched composite film thickness is in the range 2 to 150micrometers, preferably in the range about 6 to 70 micrometers.

There are no particular limitations on the length and width dimensionsof the envelope 4 except as dictated by deaeration performance desiredand availability of materials. Typically, the envelope 4 should be inthe range 10 to 100 centimeters wide and in the range 2 to 20 meterslong. As the element 1 is typically operated at a pressure differentialbetween the outside and inside of the element, the inside being at alower pressure, there are some practical limitations imposed due topressure drop across the element walls or through the interior of theelement. If the envelope is too long, it will be difficult to maintainthe desired pressure differential across the walls of the element overits full length. On the other hand, if the envelope is too short theremay not be sufficient surface area available to achieve the desired gaspermeation rate. Nevertheless, even with these considerations, there isconsiderable flexibility in choosing suitable length and widthdimensions for the envelope 4.

The nonporous fluoropolymer film envelope 4 can be made from a singlesheet as shown in FIG. 1, or can be made using two sheets of nonporousfluoropolymer film or laminate, in which case the seal region 5 extendsaround the entire periphery of the element. Alternatively, unsupportednonporous thin-walled tubes of a melt-processible thermoplasticfluoropolymer can be extruded or blow-molded and flattened to form theenvelope 4. In this case, only the ends will have a seal region 5.Sealing the open edges of an envelope 4 made of a melt-processiblethermoplastic fluoropolymer film or laminate can be readily accomplishedby application of heat and pressure at seal regions 5 where the filmoverlaps the porous gas-channel-forming component 2. Many heat sealingmethods are known in the art and can be used.

An alternative seal region 15 is illustrated in FIG. 2. In thisconfiguration reinforcing strips 6 of porous polytetrafluoroethylene(PTFE) film are placed on the outward-facing surfaces of the envelope 4at the seal region 15 prior to heat sealing. When heat sealing isperformed some of the melt-processible fluoropolymer film penetratesinto the porous PTFE film and the strength and reliability of the sealare enhanced. The porous PTFE film also serves as an excellent releasematerial which prevents contact between melted thermoplasticfluoropolymer and equipment surfaces applying heat and pressure to theseal region 15. Preferably, the porous PTFE film is porous expandedpolytetrafluoroethylene film.

The interior of the deaeration element 1 contains a gas-channel-formingcomponent 2 which provides pathways through the inside of the elementfor gases which have permeated from the liquid through the film formingthe envelope 4, to at least one port in the film envelope 4 which isconnected to means for transfer of gases to a location external to theapparatus. The gas-channel-forming component must be able to withstandthe compressive forces exerted on it, be compatible with the gases to beremoved from the liquid, and, within these limitations, have a structureas open or porous as possible so as to minimize the pressure dropthrough the interior of the element 1. Preferably thegas-channel-forming component 2 is made of a synthetic polymer, althoughother materials can also be used. Suitable polymeric material and formsare known in the art and are available commercially. Suitable materialsinclude polymers such as polyolefins, polyesters, nylons, polyurethanes,polycarbonates, polystyrenes, polyvinyl chloride, polyvinylidenechloride, and the like; or fluoropolymers such as PTFE, FEP, PFA,polyvinylfluoride, polyvinylidene fluoride, and the like. Suitable formsinclude nonwoven fabric, knit fabric, woven fabric or mesh, open-cellfoams, porous membranes, and the like. The thickness of thegas-channel-forming component 2 is preferably in the range of about 0.3millimeters to about 2 millimeters, and should have length and widthdimensions somewhat less, about 2 millimeters to about 10 millimetersless, than the length and width dimensions of the envelope 4 in order toprovide sufficient area to form the seal region 5.

When an unsupported nonporous fluoropolymer film is used to formenvelope 4, it can be desirable to laminate a porous membrane 3 to bothsides of the gas-channel-forming component 2, to form a subassembly asshown in FIG. 3; or to one side of the gas-channel-forming component 2,as shown in FIG. 4, where the subassembly is shown positioned in thefluoropolymer envelope 4 of the element 1. The porous membrane 3provides support to the nonporous fluoropolymer film forming theenvelope 4 and helps to more uniformly distribute the compressive loadon the gas-channel-forming component 2 encountered during operation. Byproviding such support to the fluoropolymer film, a thinner film can beused to form the envelope 4, thereby increasing the gas permeation ratefrom the liquid outside the element to the gas channels inside theelement. Preferably the porous membrane 3 is also made of a syntheticpolymer and its selection is subject to the same constraints listedabove for the gas-channel-forming component. Most preferred are porousmembranes of polytetrafluoroethylene such as described hereinabove.

Lamination of the porous membrane 3 to the gas-channel-forming component2 can be done using conventional methods and equipment, for example, byadhesive bonding. The adhesive can be applied to the surface to bebonded of either layer, and should be applied in a non-continuouspattern. For example, a layer applied to a surface as a pattern ofdiscrete dots, a porous non-woven web or mesh, or the like.

The adhesive may be selected from many known in the art. The adhesivecan be a thermoplastic, thermosetting, or reaction curing type, inliquid or solid form, selected from the classes including, but notlimited to, polyamides, polyacrylamides, polyesters, polyolefins,polyurethanes, and the like. The adhesive should be applied so that itforms a porous (non-continuous) gas-permeable layer which minimizesresistance to air flow while adhering the porous membrane 3 to thegas-channel-forming component 2. Preferably, the adhesive is applied soas to cover about 30 percent or less of the surface. Suitableapplication means include gravure printing, spray coating, powdercoating, interposing a non-woven web of adhesive, and the like.

Lamination of the porous membrane 3 to the gas-channel-forming component2 can be also be done using conventional heat-fusing methods andequipment, for example, by application of heat and pressure in the nipbetween rolls, or by a heated platen press, as described earlier.

One or more ports, or openings, are provided in the element 1 forpassage of gases out of the element. Transfer means, preferably a tubeof the same melt-processible thermoplastic fluoropolymer used to formthe envelope 4, for removal of gases from inside the element to alocation external to the module or apparatus in which the element 1 ispositioned is connected to the port by any convenient method. Theoutside diameter of the tube should be about 4 millimeters to about 10millimeters, and the wall thickness about 0.5 millimeters to about 1millimeter. By way of example only, one such connection is illustratedin FIG. 5.

In FIG. 5 is shown a section of one wall of the melt-processiblethermoplastic fluoropolymer film envelope 4 in which an opening 22leading to the inside of the element has been made. An end of a tube 23,preferably of the same fluoropolymer used in the envelope, is positionedaround the opening 22. A fluoropolymer ring 27 and porous PTFE film 26are pressed into place around the end of the tube 23 so that, whenfinally positioned, the film forming the envelope 4 and the PTFE film 26overlap the end of the tube 23, and the edge of the ring 27 isapproximately even with the end of the tube 23. The portion of theenvelope 4 overlapping the end of the tube 23 is heat sealed to the endof the tube by application of a heated plate (not shown) to the PTFEfilm portion overlapping the end of the tube, and a strong air-tightseal is formed. The fluoropolymer ring 27 serves as a strain relief forthe connection and also prevents distortion or contraction of theenvelope film during the heat sealing step. The porous PTFE film 26serves to reinforce the seal region and serves as a release material toprevent melted fluoropolymer from sticking to the heated plate.

To most efficiently use the element, it may be positioned in a module orapparatus in a spiral-wound configuration, as shown in FIG. 6; or in afolded configuration, as shown in FIG. 7. In such configurations a spacebetween adjacent element layers must be provided to permit the liquid tobe deaerated to contact the outer surface of the element and to permitthe liquid to flow through the module. This space can be provided byinterposing a liquid-channel-forming component 12 between adjacentlayers of the element 1, as shown in FIGS. 6 and 7. The void size anddistance between element layers provided by the liquid-channel-formingcomponent 12 should be in the range 50 to 1000 micrometers, preferablyin the range 100 to 400 micrometers. If the spacing is larger than 1000micrometers, deaeration performance will suffer as the diffusiondistance for the gas through the liquid will become too great. If thespacing is less than 50 micrometers, the pressure drop of the liquidthrough the liquid-channel-forming component may become too high. Thelength of the liquid-channel-forming component should be roughly thesame as the length of the deaeration element. The width of theliquid-channel-forming component should be at least as wide as thedeaeration element, and may be somewhat wider (about 1-2 centimeters) soas to extend beyond and protect the longitudinal edges of thefluoropolymer film envelope.

As with the gas-channel-forming component described earlier, suitablematerials include polymers such as polyolefins, polyesters, nylons,polyurethanes, polycarbonates, polystyrenes, polyvinyl chloride,polyvinylidene chloride, and the like; or fluoropolymers such as PTFE,FEP, PFA, polyvinylfluoride, polyvinylidene fluoride, and the like; informs such as nonwoven fabric, knit fabric, woven fabric or mesh, andthe like. In systems in which chemically aggressive and high purityliquids, or special liquids in which contamination must be minimized, itis preferred that the liquid-channel-forming component be made of afluoropolymer such as PTFE, PFA, or FEP.

A cross-sectional view of a deaeration apparatus or module containing aspiral-wound assembly of the invention is shown in FIG. 8. The module 41has a cylindrical casing body 41a, and end caps 41b at each end. Aspirally-wound element 1, with a liquid-channel-forming component 12interposed between adjacent layers of the element, is disposed in thecasing body. A gas removal tube 23 is connected to the element 1 andexits the module through a fitting in an end cap 41b. An inlet opening46 for a liquid to be deaerated, and a vent opening 48 for removal ofair during initial filling of the module with the liquid, are providedin one end cap. In the opposing end cap is an outlet opening 47 forliquid which has been deaerated. Optionally, porous material 49 can bedisposed between the element and end caps. The module shown is aconventional type, well known in the art, as are the materials andconstruction methods to make it, which are selected according to thefluids and operating conditions which will be encountered in theprojected end-use. Again, in systems in which chemically aggressive andhigh purity liquids, or special liquids in which contamination must beminimized, it is preferred that the module be made of a fluoropolymersuch as PTFE, PFA, or FEP, or the liquid-wetted surfaces be lined with afluoropolymer.

After the module is initially filled with a liquid to be deaerated, andtrapped air exhausted through the vent opening 48, liquid flow throughthe liquid-channel-forming component is begun and the interior of theelement 1 is operated at a pressure lower than the pressure of theliquid flowing over the outer surface of the element, for example, bydrawing a vacuum through the gas removal tube 23. Gas dissolved in theliquid, driven by the pressure differential between the liquid and theinterior of the element, diffuses out of the liquid and permeatesthrough the fluoropolymer film forming the envelope of the element,passes through the gas channels formed inside the element to the gasremoval tube, and thence out of the module. At the same time, thedissolved gas concentration in the liquid becomes progressively lower asthe liquid flows over and past the surface of the deaeration element.

The deaeration assembly of the invention accomplishes the efficientremoval of gases dissolved not only in ordinary liquids such as water oraqueous solutions, but also in chemically aggressive, high purity, andother special liquids, while contributing virtually no contaminants tothe liquids.

Referring to FIGS. 9 and 10, another embodiment of the deaerationassembly of the invention is shown. The second embodiment differs fromthe embodiment described hereinabove in that: i! both theliquid-channel-forming component and gas-channel-forming component areenclosed within the fluoropolymer film envelope of the element, ii! theliquid-channel-forming component is contiguous with at least oneinward-facing surface of the fluoropolymer film, iii! in use, thefluoropolymer film is drawn inward and conforms to the contours of theliquid-channel-forming component thereby creating channels along theoutward-facing surface of the fluoropolymer film, and iv! theliquid-channel-forming component does not come in contact with theliquid to be deaerated. In other respects, the second embodiment is thesame as the embodiment described earlier.

FIG. 9 shows an element 51 consisting of a gas-channel-formingsubassembly 52 of a porous membrane laminated to each side of agas-channel-forming component (as depicted in FIG. 3), and aliquid-channel-forming component 53 of a porous ribbed material, eachcomponent contiguous with an inward-facing surface of an envelope 54 ofa nonporous fluoropolymer film. The ribbed material of theliquid-channel-forming component can be, for example, a knitted ribbedfabric of synthetic polymer fibers. In operation, the pressuredifferential between the outside and the inside of the element causesthe inward-facing surface of the fluoropolymer film contiguous with theliquid-channel-forming component to contact and generally conform to thecontours of the liquid-channel-forming component 53 to form channels 55,defined by the ribs of the material, for passage of liquids over theoutward-facing surface of the element 51.

FIG. 10 shows sections of adjacent element layers 61 of anotherdeaeration element in which both the gas-channel-forming subassembly 62and liquid-channel-forming component 63 of a woven material arecontained within the fluoropolymer film envelope 64. The woven materialof the liquid-channel-forming component can be, for example, a wovenfabric or mesh of synthetic polymer fibers. As noted above, inoperation, the pressure differential between the outside and the insideof the element causes the inward-facing surface of the fluoropolymerfilm contiguous with the liquid-channel-forming component to generallyconform to the high spots and depressions of the woven material to formcorresponding high spots and depressions in the outward-facing surfaceto form channels 65 for passage of liquids over the outward-facingsurface of the element 61.

In this embodiment of the assembly of the invention aliquid-channel-forming component external to the element is not neededwhich significantly reduces the risk of contamination of the liquids,reduces material costs, and simplifies manufacture of the assembly.

EXAMPLE 1

On each side of a 250 micrometers thick polyester knitted fabric (StockNo. 2020, 20-denier staple fiber; made by Toray Co) was laminated a 30micrometers thick porous expanded PTFE membrane (made by Japan GoreTex,Inc.) having a pore volume of 82%. The laminate thus produced was cut tomake a gas removal subassembly 20 centimeters wide and 9 meters long ofthe type shown in FIG. 3.

The subassembly was placed on a 12.5 micrometers thick FEP film (made byDaikin Industries) which was then folded over the subassembly, and theopen ends and longitudinal edge heat-sealed to form an element about 20cm wide and 9.3 m long of the type shown in FIG. 1. An FEP tube, 6 mmoutside diameter and 4 mm inside diameter, was connected to one end ofthe element to serve as a gas removal tube. The tube was connected andheat-sealed to the element by the method shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 24 cm and a length of 9.3 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly of 101.6 mm diameter and 24 cm length which provided 3.72 m² ofsurface area for liquid contact. The deaeration assembly thus made wasinstalled in a module of the type shown in FIG. 8 which had a casingbody and end caps made of PTFE.

The deaeration assembly was tested by flowing tap-water having aninitial dissolved oxygen concentration of 8.2 ppm through the module ata rate of 300 cc/minute at 25° C. The pressure inside the element wasreduced and kept at about 100 Torr by a vacuum pump.

The dissolved oxygen concentration of the deaerated liquid at the outletof the module was measured and found to be 2.9 ppm, which is a goodvalue.

A second test under the same conditions except that tap-water containing9% neutral detergent (with surfactant) was used. The dissolved oxygencontent of the deaerated liquid at the outlet was found to be 2.95 ppm,which is also a good value.

After the second test, the module was emptied of water and filled with98% ethyl alcohol. The pressure inside the element was reduced to 100Torr. No alcohol was detected in the gas sampled from the gas removaltube, confirming that the alcohol liquid did not permeate through theFEP deaeration film.

Hot water (90° C.) was also passed through the module, after which theapparatus was disassembled and the various components inspected. Nochange whatsoever was seen in any of the materials.

It is apparent from the above that the deaeration assembly of theinvention permits deaeration of a liquid containing a surfactant, andthat there is no problem with washing the assembly with 90° C. hotwater. Furthermore since the deaeration apparatus used in this examplemakes use of FEP, PFA, or PTFE for all its liquid-wetted parts, it canalso be used with chemically aggressive liquids which are stronglyacidic or alkaline.

EXAMPLE 2

A deaeration assembly was made as described in Example 1, except thatthe FEP film was 25 micrometers thick.

The deaeration assembly was installed in the module and the same testsperformed as described in Example 1, except that the liquid flow ratewas 200 cc/minute.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 2.95 ppm, which is a good value. The results ofthe other tests were the same as described in Example 1.

EXAMPLE 3

A gas removal subassembly was made as described in Example 1.

The subassembly was placed on a 25 micrometers thick FEP film (made byDaikin Industries). A woven mesh of PFA (made by Gunze Co.), about 8mesh/cm (20 mesh/inch) and 0.51 mm thick to serve as theliquid-channel-forming component, was cut to the same width and lengthas the subassembly. The liquid-channel-forming component was placed onand aligned over the gas removal subassembly. The FEP film was thenfolded over the subassembly and liquid-channel-forming component, andthe open ends and longitudinal edge heat-sealed to form an element about20 cm wide and 9.3 m long of the type shown in FIG. 9. An FEP tube, 6 mmoutside diameter and 4 mm inside diameter, was connected to one end ofthe element to serve as a gas removal tube. The tube was connected andheat-sealed to the element by the method shown in FIG. 5.

The element, with the liquid-channel-forming component and gas removalsubassembly enclosed within the FEP film envelope, was rolled up to forma spiral-wound deaeration assembly which provided about 3.72 m² ofsurface area for liquid contact. The deaeration assembly thus made wasinstalled in a module and tested as described in Example 1.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 2.7 ppm, which is a good value. The results ofthe other tests were the same a s described in Example 1.

EXAMPLE 4

A deaeration assembly having the same structure and dimensions asdescribed in Example 1 was made, the only difference being that the FEPfilm was 25 micrometers thick and was extruded in tubular form. A jigwas prepared and the gas removal subassembly was drawn into the tube,thus only the ends of the tube required sealing. This procedure greatlysimplified and shortened the production process to form the deaerationassembly. The deaeration assembly thus made was installed in a moduleand tested as described in Example 1.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 2.95 ppm, which is a good value. The results ofthe other tests were the same as described in Example 1.

EXAMPLE 5

A deaeration assembly having the same structure and dimensions asdescribed in Example 3 was made, the only difference being that the FEPfilm was extruded in tubular form. A jig was used to simultaneously drawthe gas removal subassembly and liquid-channel-forming component intothe tube, thus only the ends of the tube required sealing. Thisprocedure greatly simplified and shortened the production process toform the deaeration assembly. The deaeration assembly thus made wasinstalled in a module and tested as described in Example 1.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 3.02, which is a good value. The results of theother tests were the same as described in Example 1.

EXAMPLE 6

On each side of a 250 micrometers thick polyester knitted fabric (StockNo. 2020, 20-denier staple fiber; made by Toray Co) was laminated a 30micrometers thick porous expanded PTFE membrane (made by Japan Gore-Tex,Inc.) having a pore volume of 82%. The laminate thus produced was cut tomake a gas removal subassembly 20 centimeters wide and 9 meters long ofthe type shown in FIG. 3.

The subassembly was placed on a 12.5 micrometers thick PFA film (made byDaikin Industries) which was then folded over the subassembly, and theopen ends and longitudinal edge heat-sealed to form an element about 20cm wide and 9.3 m long of the type shown in FIG. 1. A PFA tube, 6 mmoutside diameter and 4 mm inside diameter, was connected to one end ofthe element to serve as a gas removal tube. The tube was connected andheat-sealed to the element by the method shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 24 cm and a length of 9.3 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly of 101.6 mm diameter and 24 cm length which provided 3.72 m² ofsurface area for liquid contact. The deaeration assembly thus made wasinstalled in a module of the type shown in FIG. 8 which had a casingbody and end caps made of PTFE.

The deaeration assembly was tested by flowing tap-water having aninitial dissolved oxygen concentration of8.2 ppm through the module at arate of 300 cc/minute at 25° C. The pressure inside the element wasreduced and kept at about 100 Torr by a vacuum pump.

The dissolved oxygen concentration of the deaerated liquid at the outletof the module was measured and found to be 3.1 ppm, which is a goodvalue.

A second test under the same conditions except that tap-water containing9% neutral detergent (with surfactant) was used. The dissolved oxygencontent of the deaerated liquid at the outlet was found to be 3.14 ppm,which is also a good value.

After the second test, the module was emptied of water and filled with98% ethyl alcohol. The pressure inside the element was reduced to 100Torr. No alcohol was detected in the gas sampled from the gas removaltube, confirming that the alcohol liquid did not permeate through theFEP deaeration film.

Hot water (90° C.) was also passed through the module, after which theapparatus was disassembled and the various components inspected. Nochange whatsoever was seen in any of the materials.

It is apparent from the above that the deaeration assembly of theinvention permits deaeration of a liquid containing a surfactant, andthat there is no problem with washing the assembly with 90° C. hotwater. Furthermore since the deaeration apparatus used in this examplemakes use of FEP, PFA, or PTFE for all its liquid-wetted parts, it canalso be used with chemically aggressive liquids which are stronglyacidic or alkaline.

EXAMPLE 7

A deaeration assembly was made as described in Example 6, except thatthe FEP film was 25 micrometers thick.

The deaeration assembly was installed in the module and the same testsperformed as described in Example 6, except that the liquid flow ratewas 200 cc/minute.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 2.6 ppm, which is a good value. The results ofthe other tests were the same as described in Example 1.

EXAMPLE 8

A gas removal subassembly was made as described in Example 6.

The subassembly was placed on a 12.5 micrometers thick FEP film (made byDaikin Industries). A woven mesh of PFA (made by Gunze Co.), about 8mesh/cm (20 mesh/inch) and 0.51 mm thick to serve as theliquid-channel-forming component, was cut to the same width and lengthas the subassembly. The liquid-channel-forming component was placed onand aligned over the gas removal subassembly. The PFA film was thenfolded over the subassembly and liquid-channel-forming component, andthe open ends and longitudinal edge heat-sealed to form an element about20 cm wide and 9.3 m long of the type shown in FIG. 9. A PFA tube, 6 mmoutside diameter and 4 mm inside diameter, was connected to one end ofthe element to serve as a gas removal tube. The tube was connected andheat-sealed to the element by the method shown in FIG. 5.

The element, with the liquid-channel-forming component and gas removalsubassembly enclosed within the PFA film envelope, was rolled up to forma spiral-wound deaeration assembly which provided about 3.72 m² ofsurface area for liquid contact. The deaeration assembly thus made wasinstalled in a module and tested as described in Example 1.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 2.8 ppm, which is a good value. The results ofthe other tests were the same as described in Example 1.

EXAMPLE 9

A deaeration assembly having the same structure and dimensions asdescribed in Example 6 was made, the only difference being that the PFAfilm was 25 micrometers thick and was extruded in tubular form. A jigwas prepared and the gas removal subassembly was drawn into the tube,thus only the ends of the tube required sealing. This procedure greatlysimplified and shortened the production process to form the deaerationassembly. A degassing tube was installed and the deaeration assemblythus made was installed in a module and tested as described in Example1.

The dissolved oxygen content of the deaerated liquid at the moduleoutlet was found to be 3.1 and 3.15, which are good values. The resultsof the other tests were the same as described in Example 1.

EXAMPLE 10

The surface of a 25 micrometers thick FEP film (made by DaikinIndustries) was washed with ethyl alcohol and dried at room temperature.The washed surface of the film was treated with TETRA-ETCH® (an etchantfor fluoropolymer surfaces, made by Junkosha Corp.), then washed againwith ethyl alcohol and dried. The washed film was laminated to a 250micrometers thick polyester knit fabric (Stock No. 2020, 20 denierstaple fiber, made by Toray Co.) using an epoxy resin-based adhesive(Product. No. 3446, made by Mereko Co.) applied in a dot pattern by agravure printing roll. The laminated composite film was heated in anoven at 80° C. for 2 hours.

Two sheets of the laminated composite, 19 cm wide and 8.5 m long, weresuperposed with the FEP film on the outside and the four edges heatsealed to form an envelope-type element. An FEP tube, 6 mm OD and 4 mmID, was connected near one end of the element to serve as a gas-removaltube. The tube was connected and heat-sealed to the element by themethod shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 23 cm and a length of 8.5 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly which provided 3.2 m² of surface area for liquid contact. Thedeaeration assembly thus made was installed in a module of the typeshown in FIG. 8 which had a casing body and end caps made of PTFE. Theliquid contact distance was 19 cm, and the gaps between the liquidchannels were 0.5 mm.

The deaeration assembly was tested by flowing tap-water having aninitial dissolved oxygen concentration of 8.5 ppm through the module ata rate of 200 cc/minute at 22° C. The pressure inside the element wasreduced and kept at about 60 Torr by a vacuum pump. The differentialpressure between the water inlet and outlet of the module was 0.1kg/cm².

When the module was first operated at water pressure of 2 kg/cm² thedissolved oxygen concentration of the deaerated liquid at the outlet ofthe module was measured and found to be 3.04 ppm, which is a good value.When the water pressure was raised to 4 kg/cm² the dissolved oxygencontent at the outlet was 3.08 kg/cm², and when the water pressure wasreturned to 2 kg/cm² the dissolved oxygen concentration was 3.08 ppm,verifying that the envelope film had good strength.

A second test under the same conditions except that tap-water containing5% neutral detergent (with surfactant) was used. The dissolved oxygencontent of the deaerated liquid at the outlet was found to be 3.1 ppm,which is a good value.

After the second test, the module was emptied of water and filled with98% ethyl alcohol. The pressure inside the element was reduced to 30Torr. No alcohol was detected in the gas sampled from the gas removaltube, confirming that the alcohol liquid did not permeate through theFEP deaeration film.

Hot water (90° C.) was also passed through the module, after which theapparatus was disassembled and the various components inspected. Nochange whatsoever was seen in any of the materials.

It is apparent from the above that the deaeration assembly of theinvention permits deaeration of a liquid containing a surfactant, andthat there is no problem with washing the assembly with 90° C. hotwater. Furthermore since the deaeration apparatus used in this examplemakes use of FEP, PFA, or PTFE for all its liquid-wetted parts, it canalso be used with chemically aggressive liquids which are stronglyacidic or alkaline.

EXAMPLE 11

A 25 micrometers thick FEP film (made by Daikin Industries) waslaminated to a porous PTFE film. The porous PTFE film (made by JapanGore-Tex, Inc.) was 30 micrometers thick and had a nominal pore size of0.2 micrometer and pore volume of 85%. The films were thermally fused byapplication of heat and pressure in passage through the nip of calenderrolls at a temperature of about 295° C. to form a laminated compositefilm.

A 20 mesh (8 mesh/cm) polyester net (0.5 mm thick; 23 cm wide; 8.5 mlong) was interposed between the porous PTFE surfaces of the compositefilm and the edges heat-sealed to form an envelope-type element. An FEPtube, 6 mm OD and 4 mm ID, was connected near one end of the element toserve as a gas-removal tube. The tube was connected and heat-sealed tothe element by the method shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 23 cm and a length of 8.5 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly which provided 3.2 m² of surface area for liquid contact. Thedeaeration assembly thus made was installed in a module of the typeshown in FIG. 8 which had a casing body and end caps made of PTFE. Theliquid contact distance was 19 cm, and the gaps between the liquidchannels were 0.5 mm.

The module was tested as described in Example 10. The dissolved oxygenconcentration at the outlet was 2.45 ppm, 2.62 ppm, and 2.57 ppm atwater pressures of 2, 4, and 2 kg/cm², respectively. The results of theother tests were the same as described in Example 10.

EXAMPLE 12

The composite film prepared as described in Example 11 was stretched anamount of 3:1 in the transverse direction on a heated tenter frame at atemperature of about 285° C. The stretched composite film thickness was30 micrometers. The thickness of the FEP layer was 9.5 micrometers andthe thickness of the PTFE layer was 21 micrometers thick, indicatingthat the FEP penetrated into the surface region of the porous PTFE film.

A 20 mesh (8 mesh/cm) polyester net (0.5 mm thick; 23 cm wide; 8.5 mlong) was interposed between the porous PTFE surfaces of the compositefilm and the edges heat-sealed to form an envelope-type element. An FEPtube, 6 mm OD and 4 mm ID, was connected near one end of the element toserve as a gas-removal tube. The tube was connected and heat-sealed tothe element by the method shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 23 cm and a length of 8.5 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly which provided 3.2 m² of surface area for liquid contact. Thedeaeration assembly thus made was installed in a module of the typeshown in FIG. 8 which had a casing body and end caps made of PTFE. Theliquid contact distance was 19 cm, and the gaps between the liquidchannels were 0.5 mm.

The module was tested as described in Example 10. The dissolved oxygenconcentration at the outlet was 1.70 ppm, 1.80 ppm, and 1.74 ppm atwater pressures of 2, 4, and 2 kg/cm², respectively. The results of theother tests were the same as described in Example 10. The results are aclear indication of the improved deaeration and sufficiency of strengthprovided by the thinner fluoropolymer film envelope.

EXAMPLE 13

The surface of a 25 micrometers thick PFA film (made by DaikinIndustries) was washed with ethyl alcohol and dried at room temperature.The washed surface of the film was treated with TETRA-ETCH® (an etchantfor fluoropolymer surfaces, made by Junkosha Corp.), then washed againwith ethyl alcohol and dried. The washed film was laminated to a 250micrometers thick polyester knit fabric (Stock No. 2020, 20 denierstaple fiber, made by Toray Co.) using an epoxy resin-based adhesive(Product. No. 3446, made by Mereko Co.) applied in a dot pattern by agravure printing roll. The laminated composite film was heated in anoven at 80° C. for 2 hours.

Two sheets of the laminated composite, 19 cm wide and 8.5 m long, weresuperposed with the PFA film on the outside and the four edges heatsealed to form an envelope-type element. An PFA tube, 6 mm OD and 4 mmID, was connected near one end of the element to serve as a gas-removaltube. The tube was connected and heat-sealed to the element by themethod shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 23 cm and a length of 8.5 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly which provided 3.2 m² of surface area for liquid contact. Thedeaeration assembly thus made was installed in a module of the typeshown in FIG. 8 which had a casing body and end caps made of PTFE. Theliquid contact distance was 19 cm, and the gaps between the liquidchannels were 0.5 mm.

The deaeration assembly was tested by flowing tap-water having aninitial dissolved oxygen concentration of 8.5 ppm through the module ata rate of 200 cc/minute at 22° C. The pressure inside the element wasreduced and kept at about 60 Torr by a vacuum pump. The differentialpressure between the water inlet and outlet of the module was 0.1kg/cm².

When the module was first operated at water pressure of 2 kg/cm² thedissolved oxygen concentration of the deaerated liquid at the outlet ofthe module was measured and found to be 3.31 ppm, which is a good value.When the water pressure was raised to 4 kg/cm² the dissolved oxygencontent at the outlet was 3.35 kg/cm², and when the water pressure wasreturned to 2 kg/cm² the dissolved oxygen concentration was 3.41 ppm,verifying that the envelope film had good strength.

A second test under the same conditions except that tap-water containing5% neutral detergent (with surfactant) was used. The dissolved oxygencontent of the deaerated liquid at the outlet was found to be 3.30 ppm,which is a good value.

After the second test, the module was emptied of water and filled with98% ethyl alcohol. The pressure inside the element was reduced to 30Torr. No alcohol was detected in the gas sampled from the gas removaltube, confirming that the alcohol liquid did not permeate through theFEP deaeration film.

Hot water (90° C.) was also passed through the module, after which theapparatus was disassembled and the various components inspected. Nochange whatsoever was seen in any of the materials.

It is apparent from the above that the deaeration assembly of theinvention permits deaeration of a liquid containing a surfactant, andthat there is no problem with washing the assembly with 90° C. hotwater. Furthermore since the deaeration apparatus used in this examplemakes use of FEP, PFA, or PTFE for all its liquid-wetted parts, it canalso be used with chemically aggressive liquids which are stronglyacidic or alkaline.

EXAMPLE 14

A 25 micrometers thick PFA film (made by Daikin Industries) waslaminated to a porous PTFE film. The porous PTFE film (made by JapanGore-Tex, Inc.) was 30 micrometers thick and had a nominal pore size of0.2 micrometer and pore volume of 85%. The films were thermally fused byapplication of heat and pressure in passage through the nip of calenderrolls at a temperature of about 295° C. to form a laminated compositefilm.

A 20 mesh (8 mesh/cm) polyester net (0.5 mm thick; 23 cm wide; 8.5 mlong) was interposed between the porous PTFE surfaces of the compositefilm and the edges heat-sealed to form an envelope-type element. An PFAtube, 6 mm OD and 4 mm ID, was connected near one end of the element toserve as a gas-removal tube. The tube was connected and heat-sealed tothe element by the method shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 23 cm and a length of 8.5 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly which provided 3.2 m² of surface area for liquid contact. Thedeaeration assembly thus made was installed in a module of the typeshown in FIG. 8 which had a casing body and end caps made of PTFE. Theliquid contact distance was 19 cm, and the gaps between the liquidchannels were 0.5 mm.

The module was tested as described in Example 10. The dissolved oxygenconcentration at the outlet was 2.65 ppm, 2.84 ppm, and 2.68 ppm atwater pressures of 2, 4, and 2 kg/cm², respectively. The results of theother tests were the same as described in Example 10.

EXAMPLE 15

The composite film prepared as described in Example 14 was stretched anamount of 3:1 in the transverse direction on a heated tenter frame at atemperature of about 285° C. The stretched composite film thickness was30 micrometers. The thickness of the PFA layer was 9.5 micrometers andthe thickness of the PTFE layer was 21 micrometers thick, indicatingthat the FEP penetrated into the surface region of the porous PTFE film.

A 20 mesh (8 mesh/cm) polyester net (0.5 mm thick; 23 cm wide; 8.5 mlong) was interposed between the porous PTFE surfaces of the compositefilm and the edges heat-sealed to form an envelope-type element. An PFAtube, 6 mm OD and 4 mm ID, was connected near one end of the element toserve as a gas-removal tube. The tube was connected and heat-sealed tothe element by the method shown in FIG. 5.

A woven mesh of PFA (made by Gunze Co.), about 8 mesh/cm (20 mesh/inch)and 0.51 mm thick, was cut to a width of 23 cm and a length of 8.5 m toserve as a liquid-channel-forming component. The liquid-channel-formingcomponent was placed on and aligned over the element, and the element,with the liquid-channel-forming component interposed between layers, wasrolled up (as shown in FIG. 6) to form a spiral-wound deaerationassembly which provided 3.2 m² of surface area for liquid contact. Thedeaeration assembly thus made was installed in a module of the typeshown in FIG. 8 which had a casing body and end caps made of PTFE. Theliquid contact distance was 19 cm, and the gaps between the liquidchannels were 0.5 mm.

The module was tested as described in Example 10. The dissolved oxygenconcentration at the outlet was 1.85 ppm, 1.95 ppm, and 1.86 ppm atwater pressures of 2, 4, and 2 kg/cm², respectively. The results of theother tests were the same as described in Example 10. The results are aclear indication of the improved deaeration and sufficiency of strengthprovided by the thinner fluoropolymer film envelope.

We claim:
 1. In an apparatus, a deaeration assembly for removal of a gasfrom a liquid comprising:(a) a deaeration element having agas-channel-forming component enclosed and sealed within, but not bondedto, an envelope formed of a nonporous film oftetrafluoroethylene/(perfluoroalkyl) vinyl ether copolymer (PFA), saidenvelope having inward-facing and outward-facing surfaces and at leastone port leading from the inside to the outside of said envelope forpassage of gases permeating into the element to a location external tothe apparatus; and (b) a liquid-channel-forming component contiguouswith at least one outward-facing surface of said fluoropolymer filmenvelope, said liquid-channel-forming component providing pathways for aliquid to contact and flow over said outward-facing surface of theenvelope.
 2. The deaeration assembly for removal of a gas from a liquidas recited in claim 1 wherein said liquid-channel-forming component isformed of a fluoropolymer material.
 3. The deaeration assembly forremoval of a gas from a liquid as recited in claim 2 wherein saidgas-channel-forming component comprises at least one porous materialselected from the group consisting of nonwoven fabric, knit fabric,woven fabric or mesh, open-cell foams, and porous membranes, ofsynthetic polymers, said gas-channel-forming component having continuousinterconnected pores and passageways throughout its structure wherebypassage of gases is enabled.
 4. The deaeration assembly for removal of agas from a liquid as recited in claim 1 wherein said gas-channel-formingcomponent comprises at least one porous material selected from the groupconsisting of nonwoven fabric, knit fabric, woven fabric or mesh,open-cell foams, and porous membranes, of synthetic polymers, saidgas-channel-forming component having continuous interconnected pores andpassageways throughout its structure whereby passage of gases isenabled.
 5. In an apparatus, a deaeration assembly for removal of a gasfrom a liquid comprising:a deaeration element having agas-channel-forming component and a liquid-channel-forming componenthaving a contoured surface of higher and lower regions, said componentsenclosed and sealed within, but not bonded to, an envelope formed of anonporous film of tetrafluoroethylene/(perfluoroalkyl) vinyl ethercopolymer, said envelope having inward-facing and outward-facingsurfaces and at least one port leading from the inside to the outside ofsaid envelope for passage of gases permeating into the element to alocation external to the apparatus; wherein said liquid-channel-formingcomponent is contiguous with at least one inward-facing surface of saidenvelope, and wherein the region of said envelope in contact with saidliquid-channel-forming component conforms to the contoured surface ofthe liquid-channel-forming component to form channels in saidoutward-facing surface, said channels providing pathways for a liquid tocontact and flow over the outward surface of the envelope.
 6. Thedeaeration assembly for removal of a gas from a liquid as recited inclaim 5 wherein said gas-channel-forming component and saidliquid-channel-forming component comprise at least one porous materialselected from the group consisting of nonwoven fabric, knit fabric,woven fabric or mesh, open-cell foams, and porous membranes, ofsynthetic polymers, said gas-channel-forming component having continuousinterconnected pores and passageways throughout its structure wherebypassage of gases is enabled.
 7. In an apparatus, a deaeration assemblyfor removal of a gas from a liquid comprising:(a) a deaeration elementhaving a gas-channel-forming component enclosed and sealed within, butnot bonded to, an envelope, said envelope comprising a nonporousfluoropolymer film laminated to a porous polytetrafluoroethylenemembrane; said envelope having porous inward-facing surfaces andnonporous outward-facing surfaces, and at least one port leading fromthe inside to the outside of said envelope for passage of gasespermeating into the element to a location external to the apparatus; and(b) a liquid-channel-forming component contiguous with at least oneoutward-facing surface of said fluoropolymer film envelope, saidliquid-channel-forming component providing pathways for a liquid tocontact and flow over said outward-facing surface of the envelope. 8.The deaeration assembly for removal of a gas from a liquid as recited inclaim 7 wherein said nonporous fluoropolymer film is a film oftetrafluoroethylene-hexafluoropropylene copolymer.
 9. The deaerationassembly for removal of a gas from a liquid as recited in claim 8wherein said liquid-channel-forming component is formed of afluoropolymer material.
 10. The deaeration assembly for removal of a gasfrom a liquid as recited in claim 9 wherein said gas-channel-formingcomponent comprises at least one porous material selected from the groupconsisting of nonwoven fabric, knit fabric, woven fabric or mesh,open-cell foams, and porous membranes, of synthetic polymers, saidgas-channel-forming component having continuous interconnected pores andpassageways throughout its structure whereby passage of gases isenabled.
 11. The deaeration assembly for removal of a gas from a liquidas recited in claim 8 wherein said gas-channel-forming componentcomprises at least one porous material selected from the groupconsisting of nonwoven fabric, knit fabric, woven fabric or mesh,open-cell foams, and porous membranes, of synthetic polymers, saidgas-channel-forming component having continuous interconnected pores andpassageways throughout its structure whereby passage of gases isenabled.
 12. The deaeration assembly for removal of a gas from a liquidas recited in claim 7 wherein said nonporous film is a film oftetrafluoroethylene-(perfluoroalkyl) vinyl ether copolymer.
 13. Thedeaeration assembly for removal of a gas from a liquid as recited inclaim 12 wherein said liquid-channel-forming component is formed of afluoropolymer material.
 14. The deaeration assembly for removal of a gasfrom a liquid as recited in claim 13 wherein said gas-channel-formingcomponent comprises at least one porous material selected from the groupconsisting of nonwoven fabric, knit fabric, woven fabric or mesh,open-cell foams, and porous membranes, of synthetic polymers, saidgas-channel-forming component having continuous interconnected pores andpassageways throughout its structure whereby passage of gases isenabled.
 15. The deaeration assembly for removal of a gas from a liquidas recited in claim 12 wherein said gas-channel-forming componentcomprises at least one porous material selected from the groupconsisting of nonwoven fabric, knit fabric, woven fabric or mesh,open-cell foams, and porous membranes, of synthetic polymers, saidgas-channel-forming component having continuous interconnected pores andpassageways throughout its structure whereby passage of gases isenabled.
 16. The deaeration assembly for removal of a gas from a liquidas recited in claim 7 wherein said gas-channel-forming componentcomprises at least one porous material selected from the groupconsisting of nonwoven fabric, knit fabric, woven fabric or mesh,open-cell foams, and porous membranes, of synthetic polymers, saidgas-channel-forming component having continuous interconnected pores andpassageways throughout its structure whereby passage of gases isenabled.
 17. In an apparatus, a deaeration assembly for removal of a gasfrom a liquid comprising:a deaeration element having agas-channel-forming component and a liquid-channel-forming componenthaving a contoured surface of higher and lower regions, said componentsenclosed and sealed within, but not bonded to, an envelope, saidenvelope comprising a nonporous fluoropolymer film laminated to a porouspolytetrafluoroethylene membrane; said envelope having porousinward-facing surfaces and nonporous outward-facing surfaces, and atleast one port leading from the inside to the outside of said envelopefor passage of gases permeating into the element to a location externalto the apparatus; wherein said liquid-channel-forming component iscontiguous with at least one inward-facing surface of said fluoropolymerfilm envelope, and wherein the region of said fluoropolymer filmenvelope in contact with said liquid-channel-forming component conformsto the contoured surface of the liquid-channel-forming component to formliquid channels in said outward-facing surface, said channels providingpathways for a liquid to contact and flow over the outward-facingsurface of the envelope.
 18. The deaeration assembly for removal of agas from a liquid as recited in claim 17 wherein said nonporousfluoropolymer film is a film of tetrafluoroethylene-hexafluoropropylenecopolymer.
 19. The deaeration assembly for removal of a gas from aliquid as recited in claim 18 wherein said gas-channel-forming componentand said liquid-channel-forming component comprise at least one porousmaterial selected from the group consisting of nonwoven fabric, knitfabric, woven fabric or mesh, open-cell foams, and porous membranes, ofsynthetic polymers, said gas-channel-forming component having continuousinterconnected pores and passageways throughout its structure wherebypassage of gases is enabled.
 20. The deaeration assembly for removal ofa gas from a liquid as recited in claim 17 wherein said nonporousfluoropolymer film is a film of tetrafluoroethylene-(perfluoroalkyl)vinyl ether copolymer.
 21. The deaeration assembly for removal of a gasfrom a liquid as recited in claim 20 wherein said gas-channel-formingcomponent and said liquid-channel-forming component comprise at leastone porous material selected from the group consisting of nonwovenfabric, knit fabric, woven fabric or mesh, open-cell foams, and porousmembranes, of synthetic polymers, said gas-channel-forming componenthaving continuous interconnected pores and passageways throughout itsstructure whereby passage of gases is enabled.
 22. The deaerationassembly for removal of a gas from a liquid as recited in claim 17wherein said gas-channel-forming component and saidliquid-channel-forming component comprise at least one porous materialselected from the group consisting of nonwoven fabric, knit fabric,woven fabric or mesh, open-cell foams, and porous membranes, ofsynthetic polymers, said gas-channel-forming component having continuousinterconnected pores and passageways throughout its structure wherebypassage of gases is enabled.